Cathode ray tube having improved deflection field forming means



H. B. LAW

March 15, 1966 CATHODE RAY TUBE HAVING IMPROVED DEFLECTION FIELD FORMING MEANS 3 Sheets-Sheet 1 Filed July 7, 1959 FS. n 5S.- Nm.

l l. -Il I l Ik nl l HHRDLD B. Law BY 772%.

H. B. LAW

March 15, 1966 CATHODE RAY TUBE HAVING IMPROVED DEFLECTION FIELD FORMING MEANS 3 Sheets-Sheet 2 Filed July '7, 1959 ik 42 a a jaa INVENTUR. HHRDLD B. Law Bv www@ A H. B. LAW

March l5, 1966 CATHODE RAY TUBE HAVING IMPROVED DEFLECTION FIELD FORMING MEANS Filed July 7, 1959 5 Sheets-Sheet 3 United States Patent O 3,240,972 CATHDE RAY TUBE HAVING IMPROVED DEFLECTIN FIELD FORMING MEANS Harold B. Law, Princeton, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed July 7, 1959, Ser. No. 825,531 8 Claims. (Cl. 313-79) This invention relates to cathode ray tubes of the postdeflection acceleration type and particularly to a novel electrode design and arrangement giving improved operational characteristics.

In cathode ray tubes wherein the electron beam is scanned over a phosphor screen, various means have been devised for the purpose of reducing the power or voltage required by the deiiection means. Prior art devices utilize electrode `arrangements which permit scansion deflection of a relatively low velocity electron beam. Following such deflection, the beam is accelerated toward the screen of the tube. In one form of such tube a multiapertured, or grid, electrode is closely spaced from the screen and is substantially coextensive therewith. Such prior art tubes have one or more of certain disadvantages which include: (a) high cost of fabricating and diticulty in supporting the grid electrode, (b) loss of resolution due to the fact that the electron beam traverses the major length of its path at relatively low velocities, (c) the presence of a shadow pattern of the grid electrode on the screen because of its physical proximity thereto, and (d) poor picture contrast due to low velocity secondary electrons from the grid electrode being attracted to the screen and, also, high velocity back scatter electrons from the screen being repelled back onto the screen by the grid electrode.

Accordingly, it is an object of my invention to provide an improved post-deflection acceleration type cathode ray tube having a novel electrode structure which avoids the disadvantages of the prior art as noted above.

Another object of my invention is to provide an improved post-deection acceleration type cathode ray tube having a novel electrode structure which, while providing low power beam deflection, als-o provides correction of raster distortion occasioned by other existing conditions.

Another object of my invention is to provide an improved post-deection acceleration type cathode ray tube having improved scan sensitivity.

Briefly, according to my invention I provide a cathode ray tube having an electron gun adapted to project a relatively low velocity electron beam through a beam deflection region and toward a phosphor screen electrode. Immediately adjacent the beam deflection region and between it and the screen is disposed a multi-apertured grid electrode transversely of the projected beam path. The multi-apertured` grid electrode is preferably dome-shaped and opened toward the beam source. It is preferably included as an element of the electron gun and is disposed within or within proximity of a conventional neck portion of the vacuum envelope of the tube.

In the drawings:

FIG. 1 is `a longitudinal section view partially in schematic of a cathode ray tube made according to my invention;

FIGS. 2 and 3 are longitudinal section and end elevation views respectively of the multi-apertured electrode of the tube of FIG. 1 according to my invention;

FIGS. 4-8 are views of other multi-apertured electrode embodiments of my invention;

FIG. 9 is a graph showing the manner in which the deflection power for the tube of FIG. 1 varie-s with the ratio of multi-apertured electrode potential to phosphor screen potential;

3,240,972 Patented Mar. l5, 1966 FIGS. 10, l1, and 12 are schematic views of various forms of multi-apertured grid electrodes according to the invention together with plots of the equipotential electric elds resulting therefrom;

FIGS. 13 and 14 are graphs showing comparative operational characteristics of different embodiments of the invention; and

FIG. l5 is a longitudinal section view in schematic of another cathode ray tube embodiment of my invention.

In FIG. 1 a cathode ray tube 10 includes a vacuum tight envelope 12 having a neck 14, a faceplate 16, and an interconnecting intermediate cone 18. The envelope 12 is closed at the free end of the neck 14 by a stem 20 through which a plurality of lead-ins 22 are sealed.

Houscd within the neck `14 is an electron gun 24 capable of forming and projecting an electron beam toward a phosphor screen 26 coated on the inside surface of the faceplate 16. An electron permeable conductive coating 27 such as evaporated aluminum is provided on the exposed surface of the screen 26. The electron gun 24 includes a cathode 28, 'a control electrode 30, a screen electrode 32, a rst anode 34, and a second anode 36. The electrodes 30, 32, 34, and 36 are mounted in spaced relation by studs 38, which are xed to the electrodes and bonded into a plurality, eg., two, glass rods 40 of which only one is shown. A magnetic deflection yoke 42 is disposed in known manner around the neck 14 adjacent the cone 18 for the purpose of deflecting the electron beam so as to scan the beam over the screen 26 as desired, for example, in a raster. A conductive coating 44 is provided on the internal surface of the cone 18 and extends to the phosphor screen 26 and into the near end of the neck 14.

In accordance with the invention, a multi-apertured grid electrode 46 is disposed immediately adjacent the primary beam deflection region or zone 48 and between this region and the phosphor screen 26 in the beam path. The multi-apertured grid electrode 46 is preferably of a dome shape and is disposed with its concave surface facing the principal deflection region 48. For purposes of simplicity of tube fabrication, the grid electrode 46 is preferably provided `as a part of the gun mount 24. Accordingly, it is supported by studs 38 on the glass rods 40. Such fabrication permits `the grid electrode 46 to be inserted into the tube 10 through the neck 14 thereof along with the other ones of the electron gun elements. Accordingly, separate support means is not required.

Various ones of the lead-ins 22 extend through the stern and connect in known `manner `to the various elements of the electron gun 24 including the novel multiapertured grid electrode 46 of the invention. The conncctions are not shown. The multi-apertured grid electrode 46 may be provided in various forms as hereinafter described, but for purposes of brevity will for all forms be referred to herein simply as a grid or grid electrode.

FIGS. 2 and 3 illustrate one form of the grid electrode 46 preferred for certain applications according to my invention. The grid electrode 46 comprises a metal support ring 52 across which a multi-apertured member 54 is mounted. The multi-apertured member 54 may be secured to the ring 52 in any suitable manner, such as brazing or clamping between a pair of mating ring elements. The multi-apcrtured member 54 of the particular grid electrode 46 is dome-shaped with a substantially spherical contour and with the dome thereof comprising slightly less than a complete hemisphere.

Other grid electrode shapes suitable for certain applications of my invention are shown in FIGS. 4-7. FIGS. 4 and 5 show a dat multi-apertured structure 56 mounted across a support ring 52. FIGS. 6 and 7 show a reverse-curved multi-apertured structure 58 mounted across a support ring 52. The reverse-curved grid structure 58 resembles a spherical dome Whose edge portion 60 is outwardly flared. The functional qualities of the three grid shapes shown in FIGS. 2-7 will be hereinafter described and compared.

My invention is not limited in scope to any particular multi-apertured type structure or fabrication techniques. I prefer to use an extremely fine grid structure of, for example 500 openings per inch. The multi-apertured members 54, 56, or 58 may consist of a woven mesh. an electro-formed integral cross grid structure, an apertured plate, or other various constructions. In order to form a spherical dome-shaped structure such as the grid electrode 46 of FIGURES l, 2, and 3 from a flat multiapertured structure, known forming methods may be used. For example, a flat multi-apertured structure may be spherically formed by pressing it into a spherically contoured mold with a mating ball. After being so formed, the resulting grid 54 may be trimmed and the formed portion mounted on the support ring 52.

One form of multi-apertured structure, which for some considerations is preferred, is shown in FIG. 8 to comprise a spherically curved plate 62 having a multiplicity of tapered apertures 64 therethrough. 1n the drawing, for clarity, the tapered apertures 64 are greatly exaggerated in size compared to the size of the plate 62. Such a grid structure might be fabricated by a photo-etching of the apertures. This type grid structure provides apertures having a knife-edge as viewed from thc side of the small diameter thereof. When such a grid is disposed with its knife-edge side facing the electron gun of the tube, emission of secondary electrons by the grid is more effectively confined to the electron gun side thereof and thus is less detrimental to screen contrast.

In operation of the tube l suitable voltages are applied to the electrodes inside the envelope 12 so as to produce an electron beam 50 characterized by a relatively low velocity as it passes through the deflection region 48. Thus, with suitable voltages applied to the grid electrode 46 and to the conductive coating 44 and phosphor screen coating 27, the electron beam 50 will undergo scansion deflection at a relatively low beam velocity within the deflection region 48 and then, after passing through the grid electrode 46, be accelerated to impinge upon the phosphor screen 26 at a relatively high velocity.

The electron gun 24 of FlG. 1 is one type of gun suitable for use with my invention. The gun 24 is one of the type known as inverse focus guns. Suitable voltages for operating the gun 24 with my invention are shown by the schematic leads and arrows of FIG. l.

The high voltage on the first anode 34 serves to accelerate the electron beam as it emerges from the control electrode 30. Then the relatively low voltage on the second anode 36 causes the beam to be deceleratcd and pass through the principal deflection region 48 at a relatively low velocity. After the beam passes through the grid electrode 46, which is also maintained at a relatively low potential, it is rapidly accelerated to the screen by the relatively high potential on both the screen 26 and the wall coating 44 of the cone 18. It will be appreciated that by virtue of the high potentials on the first anode 34 and the wall coating anode 44, the electron beam is maintained at a relatively low velocity only in the vicinity of the principal deflection region 48. Thus, loss of beam resolution due to long transit time as encountered in some prior art tubes is reduced. Since the screen electrode 32, the first anode 34, and the second anode 36 bear alternately low, high, and low potentials, electrostatic lenses are formed between these electrodes and serve to focus the electron beam.

According to the preferred embodiment and mode of operation of the invention, the second anode 36 is operated slightly positive relative to the grid electrode 46. A potential difference of from 100 `to 300 volts has been found to be satisfactory. Under these conditions, secondary electrons emitted by the grid electrode 46 are attracted to and collected by the anode 36. This, of course, prevents such electrons from impinging on the screen 26 and causing a decrease of contrast. Stlch an advantageous result is not found with the prior art type tubes wherein a large grid electrode is placed adjacent the screen. In such prior art tubes it is not feasible to satisfactorily collect secondary electrons emitted from the grid electrode.

Since the anode 36 is disposed between the beam path and the deflection yoke 42, it must be of suitable nonmagnetic material so as not to distort the deflection fields of the yoke. Moreover, the anode 36 should be highly resistive so as to minimize eddy current losses. For this purpose the anode 36 can, for example, be made of. a high resistance material such as Nichrorne, or made thin, or slotted.

The effect of the grid electrode 46 upon deflection of the electron beam is best shown with reference to FIG. 9. In the graph of FIG. 9, the ratio of voltage on the grid electrode 46 to the voltage on the screen 26 is plotted as an ordinate. The abscissa of this graph represents the percentage of deflection power required for full horizontal deflection by the yoke 42 as compared with a commercial prior art cathode ray tube not employing post acceleration of the electron beam. The curve 66 shows that with five kilovolts on the grid electrode 46 and twenty kilovolts on the screen 26 as shown in FIG. 1 (or a grid/screen ratio of potentials of 0.25) the deflection obtained requires only approximately 15% of the deflection yoke power required to produce comparable deflection in this prior art cathode ray tube. The curve also shows that, as the grid potential is raised to equal the screen potential thus giving a ratio of 1.0, the same amount of power is required as in the commercial kinescope. I have found that a grid-toscreen potential range of ratios of approximately 0.2 to 0.6 is suitable for good results.

A cathode `ray tube of my invention achieves the advantage of low power deflection found in the post-deflection acceleration class of cathode ray tubes. However, at the same time it avoids the disadvantages present in the prior art tubes of this class. Comparing the tube of the present invention with the disadvantages of the prior art tubes of this class hereinbefore described, it is apparent that: (a) the cost of fabricating and the difficulty of supporting the grid electrode 46 is negligible compared with fullscreen size grid of the prior art because of the relatively small physical size of the grid 46; (b) beam resolution as affected by low velocity travel is not as detrimental as in prior art tubes since the beam traverses the major portion of its path through the cone 18 of the envelope at an accelerated velocity, rather than at the relatively low velocity as is the case in the prior art tubes; (c) no shadow pattern on the screen 26 is caused by the grid electrode 46 because of its relatively great spacing therefrom; and (d) poor picture contrast due to secondary electrons from the grid and back-scatter electrons from the screen is largely avoided since secondary electrons from the grid can be collected by the tubular electrode 36 and most back-scatter electrons are free to leave the screen 26 and be collected by the cone coating electrode 44 rather than being repellcd back onto the screen as is the case with prior art tubes in which the low-voltage operating mesh is disposed adjacent thereto.

Insofar as the advantage of low power deflection with post-deflection acceleration type cathode ray tubes is concerned, the grid electrode 46 according to my invention may be any convenient shape, even planar as described above. Its function and corresponding physical requirements are that it be an electron transparent, potential bearing, shield electrode to prevent the high voltage screen potential from accelerating the electron beam through the principal deflection region 48.

However, unlike prior art tubes, the grid electrode 46 `according to my invention may serve two new functions which prior art electrode arrangements do not perform. Both of these additional functions, or purposes, are dependent upon the shape of the grid electrode 46. For such purposes the shape of the grid will be determined by characteristics inherent in the particular tube or tube type to which my invention is applied, and by the purposes which the grid is designed to achieve.

One of these two additional functions of the grid 46 is that of producing a radial electrostatic deflection field for the purpose of supplementing the principal deliection eld provided by the yoke 42 thus increasing deection sensitivity. Establishing such a supplementary radial deiiection field can be attributed to the formation of what might be considered half of a simple electron lens established between the principal yoke deflection region and the screen.

As is well known, a simple electron lens consists of two portions, one of which is convergent, and the other of which is divergent. Of these two, the former portion is always the stronger-or more effective-and accordingly produces an overall convergent lens. If the grid electrode 46 were to be removed from the tube 10 of FIG. 1, such a lens would be formed between the anode 36 and the coating anode 44 since they are operated at different potentials. However, by including the grid electrode 46 between these two anodes, and operating it substantially at the lower of the voltages on these anodes, formation of the convergent portion of the otherwise simple lens is substantially prevented. Thus, only the divergent portion, or half, of the lens remains and thus provides a substantial outward or divergent radial defiection force which supplements the principal deection force provided by the yoke 42.

This means that either the total tube length can be shortened since an additional detiection force is provided which functions along a portion of the beam path through the cone 18, or that the power input to the deflection yoke 42 may be even further reduced thus lowering the power requirements.

Another novel function, and advantage, of the grid electrode 46 is that various forms of raster distortion, such as pincushioning, can be corrected by suitably shaping the dome of the grid electrode 46. By selectively shaping the electrode 46, a desired nonuniform shape can be given to the electrostatic field between the grid electrode 46 and the wall coating anode 44. This field can then be designed to nonuniformly supplement the yoke detiection so as to compensate for raster distortion caused by other factors. For example, it is known that magnetic deflection yokes are specially Wound in order to avoid the yoke itself introducing a pincushion distortion to the raster. This is done at considerable expense. However, according to my invention, a simple yoke design can be economically utilized, and the pincushioning caused thereby may be corrected by suitably shaping the grid electrode 46. This shaping, of course, can be done at little or no added cost. Thus, a considerable saving in manufacturing cost can be achieved. How this correction and savings in cost may be realized according to my invention is further explained below.

FIGS. -14 inclusive illustrate the field shapes and the effect of three different representative grid shapes on the functions of raster shape and raster size. FIGS. 10-12 inclusive illustrate respectively, in schematic, various beam paths as effected by the equipotential electrostatic field lines established between a grid electrode of given shape and a coating electrode 44. In FIGS. 10-12 the fiat, spherical, and reverse-curve grid shapes of FIGS. 4, 2, and 6, respectively, are considered.

In FIG. 10 portions of the neck 14 and cone 18 of a cathode ray tube are shown. The fiat mesh 56 is illustrated as establishing in conjunction with the wall coating 44, equipotential lines 70. Three beam paths 72 are shown as representative of the electron beam deflected by means such as the yoke 42. As the electrons of the beam paths 72 penetrate the flat grid S6, the paths are bent strongly toward the longitudinal axis of the tube by the electric field established between the grid electrode S6 and the wall coating 44. Since the force on the electrons is normal to the equipotential lines 70, this bending is increased toward the outer edge of the grid 56 because the angle of incidence to the equipotential lines 70 is increased. On the other hand, in moving away from the fiat grid 56 after passing therethrough, the electron beam paths start to bend radially outward instead of inward because of the curvature of the equipotential lines 70. Accordingly, the ultimate landing position of the electrons of the beam paths 72 on the phosphor screen is determined by the resultant action of, first, an inward force and, later, an outward force.

Two observations have been made that concern this landing position. One is that in the case of a flat grid the initial inward force just beyond the grid structure overrides the later outward force. This effect is demonstrated by increasing the screen-to-grid potential ratio for a constant grid potential and noting that the raster on the screen is made smaller. This can be explained by the fact that the inward and outward forces, which produce a resultant inward force, become stronger as the ratio of screen-to-grid potential is increased. Thus, an increase in this ratio indicates which is the stronger or overriding force. FIG. 13 shows a plot (curve 92) of the data taken in this regard.

The second observation is that the resultant of the forces causes an increase in radial deiiection with an increase in radius as evidenced by the fact that the raster is pincushioned. This effect is illustrated in FIG. 14, which shows a plot, curve 94, of the pincushion effect as a function of screen-to-grid voltage ratio. In FIG. 14 the measure of pincushioning is determined by the radius of curvature of the edge of the raster.

FIG. 11 schematically illustrates portions of an electron tube similar to that illustrated in FIG. 10 except that that the spherically curved grid electrode 46 of FIGS. 2 and 3 is incorporated therein. The grid electrode 46, although spherical in contour, is slightly less than a complete hemisphere. From FIG. l1 it can be seen that the electron beams 74 approach the grid 46 almost normal thereto so that the initial radial force inward on the beam as the beam passes through the mesh is quite small. This is in contrast to the rather drastic inward force experienced by the beams in passing through the flat grid 56 of FIG. 10. The later outward radial force experienced by the electrons as they continue to cross the equipotential lines 76 thus easily overrides any inward force experienced adjacent to the grid 46. The graph 96 of FIG. 13 shows that for a spherical grid raster size increases with an incease of screen-to-grid potential ratio.

FIG. 14 illustrates that the effect on raster shape as characterized by pincushioning still exists in the case of the spherical grid 46. However, a comparison of the curve 94 for the fiat grid with the curve 98 for the spherical grid indicates that in the latter case such raster distortion is not as pronounced.

FIG. 12 illustrates portions of an electron tube similar to that illustrated in FIGS. 10 and 11 except that the reverse-curved grid electrode 58 of FIGS. 6 and 7 is incorporated therein. This shape grid electrode has proved capable of effecting virtually no raster distortion whatsoever. In other words, the raster formed in a tube with a given grid electrode of the reverse-curved variety may be made a substantially true production as directly inuenced by the primary yoke deflection means. In FIG. 12, as shown by the beam paths 78, near the edge of the grid the curvature is such that the beam meets it at a relatively large angle of incidence compared to the central regions thereof. Therefore, the deflection obtained at the edge is less than that near the center. Another way of analyzing the action produced by the reverse-curved grid 58 of FIG. 12 is by comparing it with the flat grid 56 of FIG. 10. While the reverse-curved grid 58 possesses the field-forming features similar to those of the flat grid 56 near its edges, it avoids the severe inward deflection of electrons near the central regions thereof by incorporating a spherical rather than a fiat contour such as shown at the center of the grid. Thus, compared to the flat grid, the reverse-curved grid provides a more uniform deflection force across a diameter thereof. The antipincushioning effects of the reverse-curved grid 58 can therefore be appreciated since it is nonuniformity of radial deflection forces which contribute to pincushioning.

A reverse-curved grid such as the grid 58 can moreover be suitably shaped to cause a barreled raster, i.e., the opposite of a pincushion raster. Accordingly, such a grid can be designed for a particular tube or tube type in conjunction with a simply wound deflection coil to compensate for pincushion distortion caused by the deflection coil as mentioned hereinbefore.

Although FIGS. 10-14 have been discussed with regard to raster distortion, it will be appreciated that the various types of grid curvatures herein illustrated also serve to demonstrate the effect of the supplemental electrostatic deflection feature of my invention. This feature, which may be termed scan or deflection magnification, is dependent both upon the spacing of the grid from the deflection yoke 42 and upon the shape of the grid.

Regarding the spacing, deflection magnification is, in general, greater the further the grid electrode is spaced beyond the yoke. Greater spacing provides a correspondingly greater primary deflection eld prior to the electrons passing through the grid electrode where the"y travel at a relatively low velocity.

Because of an essentially similar action, the shape, or curvature, of the grid will also affect the total deflection. For example, compare the tlat grid of FIG. 10 with the spherical grid of FIG. 11. In the spherical grid 46 the length of the three electron paths 74 are substantially equal and thus subject to substantially equal deflection by the yoke. On the other hand, in the case of the flat grid 56 of FIG. 1t), the three electron paths 72 are of substantially different length from the center of deflection (their common point) to the grid 56 and are thus unequally affected by the deflection field of the yoke. This nonuniformity can be utilized to obtain increased deflection, or scan magnification, at a particular desired portion of the raster relative to the other portions thereof.

Another influence of grid shape upon the electrostatic field established between the grid and wall coating electrode 44 is clearly indicated by the two curves 92 and 96 of FIG. 13. For a given screen-to-grid potential ratio a decided difference is noted between the raster sizes of a flat grid tube and a spherical grid tube. The two curves indicate that a greater supplemental deflection is provided by a spherical grid.

As suggested by the two curves of FIG. 13, a grid curvature can be established for any particular tube of given characteristics to `achieve substantially invariant picture size with screen potential variation. This feature is of special advantage in the operation, for example, a color kinescope of the type which depends upon differences of electron penetration of a plurality of phosphor layers to produce color modulation. In prior art tubes wherein the electron beam velocity at the phosphor screen is varied by varying the potential on the phosphor screen to thereby vary the penetration of the beam into the phosphor layers, a variation of raster size with penetration is experienced. Such a variation can be substantially obviated or reduced by a properly-shaped grid electrode incorporated into the tube according to my invention.

I have also found that in a tube using electrode structures made according to my invention I can vary the beam focus with very little effect in deflection sensitivity. I do this by varying the voltage on the second anode electrode 36 while maintaining the voltage on the grid electrode 46 constant. Hence, in tubes in which the beam is magnetically focused, a relatively inexpensive permanent magnet focusing means can be substituted for electromagnetic focusing means to provide the principal focusing force. A ne adjustment, or touch-up, of the focus field is then obtained by adjusting the voltage on the tubular electrode of the gun adjacent the novel grid electrode. For example, the gun 24 of tube 10 might be used for magnetic focus operation by electrically connecting the two anodes 34 and 36 together and adding suitable magnet focusing means alongside the yoke 24. The fine adjustment, or touch up, can then be obtained by adjusting the voltage on the two tubular anodes 34 and 36.

Another advantage of my invention is the possibility of employing dynamic focus correction which can be varied with the scan. A tuck-up signal voltage can be applied to the tubular electrode 36 such that this signal voltage varies in accordance with the scan so that the focus force applied to the beam varies with the beam spot position on the raster.

FIG. l5 illustrates in schematic form another embodiment of my invention which is desirable for certain uses. For example, in the embodiment of FIG. l5 a grid electrode S0 rather than forming a part of the electron gun is supported further out along the beam path on the cone 18. Such an arrangement permits an extension of the principal deflection field 48 such that advantage may be taken of the fringe portions thereof. Also, since grid mounting stucture in the neck 14 is avoided, greater primary deflection by the yoke can be provided. MaXimum deflection angle by the yoke without encountering some obstruction to the beam is determined by the diameter of the neck rather than same smaller diameter of grid mounting structure in the neck. In the embodiment of FIG. 15 the grid electrode 80 may comprise a domeshaped grid structure 82 mounted on a frusto-conical ring 84 which is fixed to the cone 18 such as, for example, by cementing thereto. In such an arrangement the grid electrode is fixed in place before the faceplate (not shown in FIG. l5) is attached to the neck 14. The tube seal may be made around the cone 18 any place between the faceplate and the electrode 80 according to known practices.

It will be appreciated by those skilled in the art that many various spherically nonsyrnmetrical grid shapes may be used to obtain special conditions of beam deflection. For example, a half cylindrical grid or variation thereof may be employed to affect the deflection in one direction only. Other special shapes will be suggested to those skilled in the art for particular requirements.

What is claimed is:

1. A cathode ray tube comprising a vacuum-tight envelope having a neck portion, a faceplate portion, and an interjacent cone portion; means disposed within said neck for projecting an electron beam toward said faceplate through a beam deflection region to scan said beam over said faceplate portion, a screen electrode on said faceplate, a conductive coating electrode on said cone portion, and dome-shaped grid electrode means disposed adjacent said deflection region and between said region and said screen with the concave side thereof facing said deflection region for electrically shielding said region from said screen and for providing in co-operation with said conductive coating electrode a raster-distortion-correction electrostatic field.

2. A cathode ray tube comprising a target electrode, means for projecting an electron beam toward said target electrode through a beam deflection region to scan said beam over said target, multi-apertured grid electrode means disposed adjacent said deflection region between said region and said target in the path of said beam for electrically shielding said region from said target, and a hollow cylindrical electrode disposed adjacent said multiapertured grid electrode means and between said multiapertured grid electrode mcans and said electron beam projecting means.

3. A cathode ray tube comprising a target electrode, means for projecting an electron beam toward said target electrode through a beam deflection region to scan said beam over said target, terminal means for applying a high positive potential to said target, multi-apertured grid electrode means disposed adjacent said deflection region between said region and said target in the path of said beam for electrically shielding said region from said high positive target potential, a hollow cylindrical electrode disposed adjacent said multi-apertured grid electrode means and between said multi-apertured grid electrode means and said electron beam projecting means, and means for mounting said multi-apertured grid electrode and said hollow cylindrical electrode in mutual electrical insulated relation whereby sad hollow cylindrical electrode may be electrically biased relative to said mutiapertured grid electrode.

4. An electron gun structure comprising insulator support means, and electron emitting means, electron modulating means, electron accelerating means, a tubular secondary-emission-electron-collector electrode and a dome-shaped grid electrode, all coaxially mounted in the order named along said insulator support means with the concave side of said grid electrode facing said tubular electrode.

5. A cathode ray tube comprising an electron gun for directing a beam of electrons through a screen scanning zone of deflection, a screen for receiving said electrons, and a multi-apertured electrode adapted to have a low positive potential applied thereto positioned adjacent said zone of deflection and between said zone of deflection and said screen to provide a low velocity beam path between said gun and said multi-apertured electrode, said multiapertured electrode having a reverse-curved section in a plane parallel to the axis of said tube, said screen being adapted to have a comparatively high positive voltage applied thereto for accelerating and further detlecting said beam.

6. A cathode ray tube comprising a vacuum-tight envelope having a neck portion, a faceplate portion, and an interjacent cone portion; means disposed within said neck for projecting an electron beam toward said faceplate through a beam deflection region to scan said beam over said faceplate portion, a screen electrode on said faceplate, a conductive coating electrode on said cone portion, and dome-shaped grid electrode means disposed adjacent said deflection region and between said region and said screen with the concave side thereof facing said detlection region for electrically shielding said region from said screen and for providing invariant raster size with variation of the velocity of said electron beam :1t said phosphor screen.

7. A cathode ray tube comprising a target electrode, means for projecting an electron beam toward said target electrode through a beam deflection region to scan said beam over said target, and reverse spherically curved dome-shaped multi-apertured grid electrode means disposed with the open side of its dome facing said detlection region and positioned adjacent said detlection region between said region and said target for electrically shielding said region from said target.

8. A cathode ray tube comprising a target electrode, means for projecting an electron beam toward said target electrode through a beam dellection region to scan said beam over said target, and dome-shaped multiapertured grid electrode means having its outer peripherr al region outwardly flared, said grid electrode means being disposed with the open side of its dome facing said detlection region and being positioned adjacent said dellection region between said region and said target for electrically shielding said region from said target.

References Cited by the Examiner UNITED STATES PATENTS 2,150,159 3/1939 Gray 315-17 x 2,176,199 10/1939 Biggs 315-17 x 2,315,367 3/1943 Epstein 315-17 x 2,718,611 9/1955 McNaney 313-86 2,735,956 2/1956 McN-aney 313-86 2,743,391 4/1956 Hoagland 315-17 2,755,413 7/1956 wagner 315-17 2,872,613 2/1959 Kalfaian 315-12 2,880,342 3/1959 Frenkei 313-85 GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner. 

4. AN ELECTRON GUN STRUCTURE COMPRISING INSULATOR SUPPORT MEANS, AND ELECTRON EMITTING MEANS, ELECTRON MODULATING MEANS, ELECTRON ACCELERATING MEANS, A TUBULAR SECONDARY-EMISSION-ELECTRON-COLLECTOR ELECTRODE AND A DOME-SHAPED GRID ELECTRODE, ALL COAXIALLY MOUNTED IN THE OTHER NAMED ALONG SAID INSULATOR SUPPORT MEANS WITH THE CONCAVE SIDE OF SAID GRID ELECTRODE FACING SAID TUBULAR ELECTRODE. 